1. Field of the Invention
The present invention relates to a method and to a device for determining the value of the flow rate of one or more phases contained in a multiphase effluent, the effluent comprising at least one gas phase and at least one liquid phase.
The invention is used to determine the mass flow rate of the phases of a petroleum effluent comprising a gas phase and a liquid phase (organic and aqueous). The effluent can possibly contain solid particles such as sand, hydrates or paraffins.
The invention is notably applied for enhanced production of a petroleum effluent by injection of gas in the string (gas lift) or by injection of steam in the reservoir. Continuous knowledge of the mass flow rate of the phases produced in each well allows optimum adjustment of the amounts of fluid injected.
2. Description of the Prior Art
Various flow metering methods and devices are known from the prior art.
Patent EP-0 674 249 describes a method and a device allowing mixing of a gas phase and a liquid phase, and to determine the value of the total flow rate of the two phases mixed in a venturi. The method requires a stage of homogenization of the two phases prior to measuring the pressure value at the inlet and at the outlet of the venturi, and a density measuring stage carried out by gammametry, which requires the presence of a radioactive source.
It is well-known to use waves such as microwaves or ultrasonic waves for determining the flow rate of the gas phase and of the liquid phase forming a multiphase effluent. U.S. Pat. Nos. 4,812,739 and 4,820,970 and French Patent 2,722,292 describe methods for determining or measuring, on the one hand, the amount of each of these phases and, on the other hand, an average velocity value or the value of the velocity for each phase, in order to respectively deduce therefrom the average total flow rate or the flow rate of each phase.
The drawback of such devices is that they are expensive and sometimes difficult to install.
The present invention is a device, flowmeter and a method which overcomes the drawbacks of the prior art.
The present invention relates to a method for determining the value of the flow rate of at least one phase forming a part of a flowing multiphase medium, the multiphase medium comprising at least one liquid phase and at least one gas phase. The invention comprises at least the following steps:
a) feeding the multiphase medium into a chamber comprising at least one delivery line, a sampling device comprising sampling ports and at least one discharge line,
b) determining at least two pressure values P1 and P2 at least at two different points A and B of the chamber and/or of the sampling device, and the internal pressure value Po,
c) determining, from the values determined in step b), from the knowledge of the density of the gas phase and of the liquid phase and/or from the average value of the density of the multiphase medium in the slotted tube, from a relation connecting at least the following parameters: GLR or the level of the interface between the liquid phase and the gas phase, from pressures P1, P2, Po, the value of the total flow rate Qt of the flowing multiphase medium and/or the flow rate of each of phases qg and ql.
According to the invention, the value of the flow rate of the gas phase and/or of the liquid phase can be determined by means of relations between the flow rates of the phases and the measured pressure differences, and notably the following relations:                               q          g                =                              S            g                    ⁢                      C            g                    ⁢                                                    2                ⁢                                  (                                                            P                      1                                        -                                          P                      0                                                        )                                                            g                ⁢                                  xe2x80x83                                ⁢                                  ρ                                      0                    ⁢                    g                                                                                                                        q          l                =                              S            l                    ⁢                      C            l                    ⁢                                                    2                ⁢                                  (                                                            P                      2                                        -                                          P                      0                                        -                                          g                      ⁢                                              xe2x80x83                                            ⁢                                              ρ                                                  0                          ⁢                          l                                                                    ⁢                                              xe2x80x83                                            ⁢                                                                        z                          2                                                2                                                                              )                                                            g                ⁢                                  xe2x80x83                                ⁢                                  ρ                                      0                    ⁢                    l                                                                                          
where
Sg and Sl correspond to the sum of the areas of the ports situated in the gas phase and in the liquid phase respectively,
z2 being the distance between the liquid-gas interface and a point,
xcfx81og and xcfx81ol being the densities for the gas and the liquid at the pressure Po and for a temperature To,
Cg and Cl being the values of the passage coefficients of the ports of the slotted tube, and the pressure values P1 and P2 being measured at the level of the sample tube.
Qt=ql+qg and GLR=qg/ql.
The value of the GLR can be determined by measuring the level of the interface between the gas phase and the liquid phase in the chamber, by taking account of the total height H of the slotted tube and of the characteristics of the sampling device such as the value of the bore coefficient of the tube, the characteristic function of the bore of the slotted tube that equips the chamber f(H,h).
The relation between the various parameters of step c) can be established by calibrating the device by varying the values of the GLR, of the differential pressures Poxe2x88x92P1 and P2xe2x88x92Po and of pressure Po, and of densities xcfx81g, xcfx81l.
The liquid phase has, for example, two liquid phases L1 and L2 of differentiable densities xcfx811 and xcfx812. A third pressure value P3 is measured in the chamber. The level of the interface between the liquid phase and the gas phase is determined for example by considering the highest liquid level in the chamber, and the value of the fraction of liquid phase L1 is determined,       W    1    =            1                        ρ          1                -                  ρ          2                      ⁡          [                                                  ρ              3                        -                          ρ              2                                            g            xc3x97            h                          -                  ρ          2                    ]      
W1=fraction of the liquid phase of density xcfx811 brought back to volume of the mixture of liquid phases. Stating from the value of W1, it is determined the value of       x    1    =            W      1              1      +      GLR      
corresponding to the fraction of the liquid phase L1, and the value of       x    2    =            1      -              W        1                    1      +      GLR      
corresponding to the fraction of the liquid phase L2 knowing the value of ql and the values of x1 and/or x2, one determines the value of flowrate qL1 and/or qL2.
The temperature and/or the pressure prevailing in the chamber can be determined and the density and/or GLR values can be corrected.
The average density xcfx81m can be determined by measuring the pressure difference between two points located a distance h apart on the slotted tube; the pressure difference can be measured in a flow element situated between the outlet of the slotted tube and the multiphase medium discharge line.
The invention also relates to a device for determining at least the value of the total flow rate of a flowing multiphase medium, the multiphase medium comprising at least one liquid phase and at least one gas phase, the device comprising a chamber provided with at least one delivery line, at least one discharge line and a sampling device comprising sampling ports for removing the liquid phase and the gas phase. The device comprises at least three pressure measuring devices, one intended to measure the internal pressure of the chamber and the two others, the pressure prevailing at two points of the chamber and/or of the sampling device, these point being located a distance d apart, a device which determines the value of the volume ratio GLR of the gas phase and of the liquid phase of the flowing multiphase medium, a processing unit which stores these measured or determined values and initially determined parameter values such as the values of the density of each phase or the average value of the density of the multiphase medium, a relation connecting at least the following parameters: the level of the interface between the gas phase and the liquid phase and/or the GLR, pressure values (P1, P2, Po), the processing unit determining at least the value of the total flow rate Qt of the multiphase medium.
The device can comprise at least one flow element situated between the outlet of the sampling device and the discharge line, the pressure measuring device being placed at the level of the flow element.
The device can comprise a device which determines the average density xcfx81m of the multiphase medium at the level of the sampling device.
The device can comprise a mixer which mixes the liquid phase and the gas phase, situated between the outlet of the sampling device and the inlet of the flow element.
The device can comprise a filter which filters the solid particles contained in the flowing multiphase medium, the filter being arranged around the slotted tube, and the chamber can have, at least at one end thereof, a shape suited to receive solid particles and a discharge of the solid particles.
The chamber may, for example, be a tube with an inside diameter xcfx86int, the slotted tube having an outside diameter xcfx86ext, the xcfx86int/xcfx86ext ratio of the diameters ranging from 1.5 to 5.
The chamber may, for example, be a tube of inside diameter xcfx86int, the slotted tube having an outside diameter xcfx86ext, and the tubes are not coaxial.
The present invention is advantageously used for determining the total flow rate Qt of a petroleum effluent comprising at least one liquid phase and at least one gas phase, and possibly solid particles.
In comparison with the devices of the prior art, the flowmeter according to the invention notably affords the following advantages:
design and operation simplicity, and therefore reduced cost, notably in the absence of densitometric measuring devices using a radioactive source,
high reliability,
easy installation in places that can be difficult to access,
possibility of associating the flow rate measurement with flow control functions within the scope of petroleum production, such as flow rate control or desanding,
possibility of estimating the production conditions of each well in real time, and possibly of correcting them automatically by acting on control devices (valves, lift flow rate, steam flow rate, etc.).